How to Fix Fault Code 37 on Onan Generator? (Error Solved!)

onan generator code 37

Fault code 37 is one of those that can have numerous causes, some of them are just awkward mistakes either by the user or technicians who have installed it in an RV.

Figuring out what has tripped this fault code is the first step to fixing it.

When you are out and away from the beaten tracks, it is very important to have a properly functioning generator as it is the only source of electricity you will have for a while.

So, how to fix fault code 37 on the Onan generator? To solve the fault code 37 on Onan generator, just check and follow the steps below:

–           Step #1: Check Summer/Winter Setting

–           Step #2: Check Regulator for Altitude

–           Step #3: Check Propane Bottle

–           Step #4: Check Spark Plug Gap

Some of the potential problems you will not be able to fix by yourself, as they require some specialized equipment for both diagnosing and fixing.

But, keep on reading to find out which causes of the fault code 37 you can fix yourself.

What is Fault Code 37 on Onan Generator

All of your appliances and devices rely on the electricity that is provided by RV’s generator fur their smooth and reliable functioning.

So, having the generator running smoothly and reliably is imperative for keeping those appliances running.

Having a generator just shut off and start blinking a fault code can be alarming, especially when you don’t know what the code means or how to fix it.

The fault code 37 means that the generator set control is not configured properly for the generator set.

Translated into simple English it means that the generator engine’s RPM and output current are not properly matched.

There are many reasons why this can happen, some of them you very likely will not be able to diagnose by yourself due to lack of proper tools, and will need to take to a proper shop.

“Some of those procedures for both troubleshooting and repairing can actually void your warranty, which why you shouldn’t want to attempt them.”

But before you do so, let’s check off the things that you actually can do by yourself.

Read also:

>> How to Fix Fault Code 12 on Onan Generator?

>> How to Fix Fault Code 14 on Onan Generator?

>> How to Fix Fault Code 13 on Onan Generator?

>> How to Fix Fault Code 15 on Onan Generator?

>> How to Fix Fault Code 36 on Onan Generator?

>> How to Fix Fault Code 33 on Onan Generator?

>> How to Fix Fault Code 32 on Onan Generator?

>> How to Fix Fault Code 22 on Onan Generator?

Reading the Fault Code on Onan Generator

Before you can fix some problem, you must make sure that it exists, in other words, you must be certain that it is a fault code 37 that your generator is showing.

Chances are that you have already established that the fault code in question is 37, but if you are not certain what is the proper procedure for checking the fault code, we’ll get through the whole process.

Onan generators have a convenient indicator light on the control switch which flashes in specific patterns depending on the fault code which has brought the generator to a halt.

This light will be displaying the code for five minutes before ceasing by itself.

In case that it has stopped blinking, you can easily retrieve the fault code with the following procedure.

  • The first thing you need is to press the STOP/PRIME button three times in quick succession. You have full five seconds after the first press to do this, so no need to hurry too much, there is plenty of time for the other two presses.
  • The indicator light will start flashing in three blinks pattern with a short pause between each set. This is known as fault code 3 which in essence indicated that some two-digit fault code has caused the generator to stop, such as fault code 37.
  • While the indicator light is flashing you need to press the STOP/PRIMER button and hold it for around a second, just counting “one-one-thousand” or “one-Mississipi” is long enough.
  • Once you release the button, it will switch to the new blinking pattern. Flashes will be divided into two groups by a short pause, first group for the first digit, second group for the second digit of the fault code. After both groups will be a longer pause, and then the flashing will repeat.

If you see the indicator light on the control switch to first blinks three times and then seven times and then going on to repeat the whole sequence after a long pause, it means that it is showing the fault code 37.

If it is actually blinking a different pattern, then you are not dealing with the fault code 37, but with some other altogether.

Keep in mind that the fault code will be flashing repeatedly for the whole five minutes, so you can let it do so several times to be certain that you are counting flashes correctly.

If you make an error when counting, you could mistake it for the fault code 38, 36, 46, 47, or 48.

One thing to keep in mind is that the first group of flashes can be between one and five, and the second between one and nine flashes, so there are no chances of confusing fault code 37 with 73.

Fault codes higher than 59 do not exist, so this flashing pattern can only be for fault code 37.

Once you have read the fault code correctly, you can either leave the generator to shut off blinking on its own after five minutes or stop it by pressing the STOP/PRIME button quickly twice.

Troubleshooting Fault Code 37

There are many causes that can lead to the fault code 37, going into details on how and with what type of tools you should go about troubleshooting them is beyond the scope of this article, and such issues are better left to professional technicians.

So, here will be covered potential issues that you can identify yourself and fix, or figure out who to blame for the problem.

Before doing any repair of the generator which is not explicitly stated in the user manual as a part of the user maintenance procedures, you should check with your dealership whether it will void the warranty or not.

Check first for the simplest solutions

The simplest problem that can cause the fault code 37 is the improper air-fuel mixture.

Whether it is lean or rich, either one can cause it.

Step #1: Check Summer/Winter Setting

So, the first thing you should check is the device that can make an impact on it, and those are the altitude setting and the season switch if your generator has it.

If your generator has a switch marked with Summer/Winter, it is for turning on and off system for preventing carburetor icing, which can throw off the proper air/fuel ratio.

Step #2: Check Regulator for Altitude

In case that you are operating the generator during temperatures below 55 degrees, it must be in winter mode, otherwise, it should be in summer mode.

“Depending on the altitude at which your RV is located it will be able to pull in the air with a differing concentration of oxygen”

Just as you can feel that it is harder for you to breathe in higher altitudes, the engine of the generator can be starved for oxygen.

This is why most Onan generators have a regulator for altitude, and you should check whether it is turned to the proper range.

Improper setting of this regulator can both lead to the air-fuel mixture being too lean or too rich, and either of them can lead to the fault code 37.

Step #3: Check Propane Bottle

Some RV dealerships like to T-split the gas line from the propane bottle into both generator and the range, after the regulator.

This is very easy to visually determine, and it is the wrong way to go about connecting the LP generator to the propane bottle.

Once your propane bottle is down to half its capacity, it will not be able to provide enough pressure for the generator, especially if you gave at least one burner on.

While the regulator of the bottle will provide the proper pressure on its outlet, the T-split will divide it into two consumers, thus it will drop.

So, the only solution you have for this is to take the RV to the dealership and having it fixed, or finding a way to have two separate propane tanks, one for the stovetop and another for the generator.

Read also: How long Does a 30 Pound Propane Tank Last In an RV?

Step #4: Check Spark Plug Gap

Another potential issue that can lead to fault code 37 is the improper gap or fouling of spark plugs, which if you have a proper socket wrench for spark plugs you can easily check and fix or replace if needs to be done.

Issues That You Can’t Fix Yourself

Proper matching of the AC frequency and RPMs of the engine is determined from the signals from magnetos and AC output.

Various issues with magnetos can lead to either improper reading of the signals, but troubleshooting them is complex and time-consuming so it’s better left for professionals.

Also, some issues with the rotor, brushes, and quad windings require a load bank for diagnosing them by pushing the generator to produce the maximum amperage, this tool you can find only in specialized shops.

And lastly, the control assembly could be faulty, and replacing it can be done only by a certified Onan dealer because replacement part is not available for purchase.

Prevent Fault Code 37 from Reoccurring

The fault code 37 can be caused by several issues, but realistically you can fix or prevent just a few of them.

Most obviously, you should always check whether your generator’s altitude setting is correct for the environment in which you are trying to use it, it is not all that hard to accidentally forget to change it.

Another setting you should be aware of is the winter/summer mode.

Keeping these two settings will make sure that your generator is getting the proper air-fuel mixture, and will prevent fault code 37 from reoccurring.

Troubleshooting an Onan Marquis Gold 5500 Generator >> Check out the video below:


Mike Gilmour

Hi, I'm Mike, co-founder, and editor of RV and Playa. My passion is traveling (with my RV) and enjoying the day at the beach (Playa)! Well, I originally created this blog as a way to share what I've learned by experimenting with the RV lifestyle, and I want to help others develop in life through new skills and opportunities.

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